1. Field of the Invention
The present invention relates to a polymeric adhesive that is capable of being made more tacky by exposure to an activating treatment, such as ultraviolet light, corona charging, etc. More specifically, the invention relates to a method of increasing the tack of a pressure sensitive adhesive by exposing an activatable, polymeric, pressure sensitive adhesive to an activating treatment. The invention also relates to activatable articles of manufacture containing such an adhesive and adhesive compositions resulting from such an activating treatment. The invention is particularly related to use of such activatable adhesives with linerless labels, enabling a user to adjust the aggressiveness of the label to meet the requirements of a particular application.
2. Description of Related Art
Pressure sensitive adhesives capable of being made more tacky by exposure to an activating treatment are known in the art. However, the adhesives described in the art are typically monomers or prepolymers that polymerize upon exposure to ultraviolet light or electron beam radiation. These monomers or prepolymers are typically applied and cured immediately on press and are not provided to the user in an uncured form. Adhesive systems using such adhesives suffer from several drawbacks.
One disadvantage of adhesive systems produced by activation of monomers or prepolymers via polymerization is the fact that the monomers or polymers are typically low viscosity fluids that are difficult to bind to a substrate, such as paper, without the use of special binders. As such, when coated onto paper these materials have a tendency to become offset onto equipment, or during handling, onto a user's hands. This can result in a loss of the adhesive material, and can create housekeeping, health and safety problems.
A second disadvantage is that applying such adhesive coatings to substrates in either a continuous or cut sheet format can cause sticking between subsequent sheets in a stack or layers in a roll, making the substrate difficult to separate.
A third disadvantage of such prior art adhesive systems is that they may have a tendency to prematurely polymerize and become undesirably tacky during storage upon exposure to light, heat, and the like.
Other adhesives described by the prior art include hot melt adhesives, which are non-tacky or slightly tacky until activated by heat. These hot melt adhesives suffer from the problem of premature activation by, for example, non-impact printing means, causing the substrate to stick to the printing apparatus or adjacent substrates to stick together.
Also known in the art are rewettable adhesives, which are non-tacky until activated by the application of moisture. Rewettable adhesives suffer from various problems, including that insufficient moisture will result in a faulty or incomplete seal, compromising the integrity of the mailer or business form with which it is used, and that substrates coated with rewettable adhesives have a tendency to curl, a phenomenon known as hygroexpansivity.
Pressure sensitive adhesives in general suffer from the problem of the adhesive having a tendency to migrate off a substrate or form and onto printing equipment. This can cause significant printer downtime for periodic cleaning to remove the adhesive.
The pressure sensitive adhesive of the invention, on the other hand, is a polymer that has sufficient viscosity and stability to be coated onto paper, stored for long periods of time, and subsequently processed by passing through a copier, non-impact printer, printing press, and the like. When desired, the paper coated with the activatable polymer can then be passed through a uv light or corona charging device to activate the adhesive. The paper can then be used, for example, as a label and can be applied to a variety of substrates by light pressure.
Another advantage of the invention is that the use of a liner can be eliminated. As a result, adhesive labels using the activatable adhesive are non-toxic and environmentally friendly, because no liner material has to be sent to a landfill, and also more cost effective because less material is used, shipped and inventoried.
An additional advantage of the invention is that, compared to traditional labels using an adhesive liner, a label incorporating the activatable adhesive of the invention achieves superior performance in a non-impact printer with respect to curl, feeding and toner adhesion.
Additional features and advantages of the invention will be set forth in the written description that follows, and in part will be apparent from the examples and written description or may be learned from the practice of the invention. The advantages of the invention will be realized and attained by the method of increasing the tack of a pressure sensitive adhesive, the activatable article of manufacture, and the pressure sensitive adhesive composition, particularly pointed out in the examples, written description and claims hereof.